Triangular Angle

Using Heron's law we get the area=(sqrt 231)/4,now we know (1/2) * 2 * 5 *sinx=(sqrt 231)/4 or 5 * sinx=(sqrt 231)/4 or sinx=(sqrt 231)/20,with calculator we get x=49.45.so round to whole number x=50(ans)

That's too simple , Directly apply cosine rule.

Here, first side=2 second side=4 third side=5 Therefore, half of perimeter s =\frac { 2+4+5 }{ 2 } Area=\frac { 2+4+5 }{ 2 } =\sqrt { 5.5\times (5.5-2)\times (5.5-4)\times (5.5-5) } =\sqrt { 5.5\times 3.5\times 1.5\times 0.5 } =\sqrt { 14.44 } =3.8 therefore, height=\frac { 2\times 3.8 }{ 5 } =1.52 therefore, sin\theta =\frac { 1.52 }{ 2 } sin\theta=0.76 \sin ^{ -1 }{ = } 50